This invention relates in general to a coil assembly and more particularly to a coil assembly that fits snuggly about a valve cartridge armature and that encounters minimal axial translation due to manufacturing tolerances.
Coil assemblies are well known. A conventional coil assembly includes a coil in the form of an insulated magnet wire wound on an insulated bobbin. The bobbin supports a pair of terminals. Lead wires of the magnet wire are wound upon the terminals. The terminals may be connected to a current source. Current passing through the magnet wire produces magnetic flux.
Conventional coil assemblies are typically used as control devices. For example, conventional coil assemblies may be used to control valves. Valves controlled by coil assemblies include an axially shiftable armature. The armature is biased by spring to maintain a valve ball in a normally opened or closed position. The valve ball is adapted to cooperate with a valve seat member, which is provided in a valve body. The armature typically slides within a valve sleeve. The coil assembly is carried by the valve sleeve.
Coil assemblies for controlling valves like the valve described above are typically enclosed by a flux return casing. An annular flux ring is often disposed within an open end of the bobbin. The annular flux ring is adapted to engage the flux return casing to complete a magnetic flux path that is adapted to pass through the armature and the valve seat member.
To actuate the valve, electric current is supplied through the terminals to the coil. The current establishes a magnetic field in the armature, which pulls the armature against the force of the spring to open or close the valve ball. An interruption in the current causes the magnetic field to collapse. This allows the spring to return the armature to its normal position.
To insure proper operation of the valve, the armature and sleeve must fit within a close tolerance of the bobbin. The bobbin must fit within a close tolerance of the flux return casing. Moreover, the annular flux ring, the flux return casing, the armature, and the valve seat member must make sufficient contact with one another.
A plurality of valves is often supported by a hydraulic control unit. Each of the valves is controlled by a separate coil assembly. The coil assemblies are typically controlled by an electronic control unit. The electronic control unit is often coupled to the coil assemblies via a lead frame or multi-chip module that is adapted to support a plurality of coil assemblies. The lead frame or multi-chip module would include a pair of holes for receiving the terminals of each coil assembly.
A problem exists with positioning the coil assemblies relative to respective valves do to manufacturing tolerances. For example, the terminals of a plurality of coil assemblies are connected to a lead frame or a multi-chip module. A plurality of valves is supported by a hydraulic control unit. Each of the coil assemblies, though connected to the lead frame or multi-chip module, must align with a corresponding valve sleeve. This often requires that a certain amount of slop exist between the coil assembly bobbins and the valve sleeves as a result of manufacturing tolerances. The slop reduces the magnetic field established in the armature. In addition, an inability to control the position of the flux return casings relative to their respective valve seats may result in insufficient contact between the flux return casings and the valve seats. This further reduces the magnetic field established in the armature.
A coil assembly is needed that fits snuggly about the valve cartridge armature and that encounters minimal axial translation resulting from manufacturing tolerances to maximize the magnetic flux through the valve armature.
The present invention is directed towards a coil assembly that meets the foregoing needs. The coil assembly comprises a coil wound upon a bobbin. A pair of terminals is supported by the bobbin. The coil has a pair of lead wires, each of which is connected to one of the terminals. Each terminal is adapted to be coupled to an electronic control unit. The coil is enclosed at least in part by a flux return casing. At least one resilient member is arranged and configured to urge the bobbin and the casing axially downward.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.